Summary
Overview
Michael Stevens and Hannah Fry explore the fundamental nature of water in this episode of The Rest is Science, challenging everyday assumptions about this familiar substance. They begin with the provocative claim that water is actually lava, explain why ice qualifies as a mineral, and reveal surprising statistics about water distribution on Earth. The discussion then traces the origins of Earth's water back to before the formation of our sun, examining how comets delivered ancient water during the heavy bombardment period. Throughout the episode, they weave in fascinating tangents about refrigeration technology and the properties of heavy water.
Water as Lava: Redefining a Familiar Substance
Stevens introduces a mind-bending concept: if ice is a mineral (which geologists officially recognize), then water is technically molten rock, or lava. This isn't just wordplay—ice meets all the criteria for being a mineral: it's inorganic, solid, and has a definite crystal structure. The fluid dynamics of actual volcanic lava behave similarly to water, with both following the same physical principles until lava cools into a toothpaste-like consistency.
- Ice qualifies as a mineral because it is inorganic, solid, and has a definite crystal structure
- A cube of ice is a monomineralic rock, making melted ice technically molten rock or lava
- Ice won the Mineral Cup in 2015 when geologists voted on their favorite mineral
- The fluid dynamics of lava and water are identical at certain stages
- Lava transitions through phases similar to water, including a toothpaste-like consistency analogous to slush
" A glass of water is actually just a glass of lava because ice is a rock "
" Everything you drink and eat is also water. Therefore, everything you consume is lava. "
The Scarcity of Drinkable Water
Despite Earth being known as the water planet, the amount of water humans can actually access and use is shockingly small. Only 2.5% of Earth's water is fresh rather than salty, and within that tiny fraction, most is locked in glaciers or underground. The water humans actually interact with—rivers, lakes, and springs—represents merely 0.0072% of all water on Earth, making it an extraordinarily precious resource hidden within multiple layers of scarcity.
- Only 2.5% of Earth's water is fresh (not salty), with the remaining 97.5% being seawater
- Almost 70% of fresh water is frozen in glaciers and ice caps
- Another 30% of fresh water exists as groundwater beneath the surface
- Only 1.2% of the 2.5% of fresh water exists on the surface
- Accessible fresh water in rivers, lakes, and springs represents just 0.0072% of all water on Earth
- All water humans use for drinking, showering, and swimming comes from this 0.0072% fraction
" Earth has a lot of water, but of all that water on the entire planet, both on it and in it, only two and a half percent is fresh, meaning not salty. "
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